Monday, September 27, 2010

Increasing Requirement on the Safety PLC

Safety PLC as the logic solver centers typically handle large amounts of Instrument Functions System, so the risk of out-of parameter control process has common elements that aim to reduce the risk. Because of the risk engineering state-of-the-art analysis does not consider the possibility of overlap and the level of risk in detail, not always obvious element whish shall be in accordance with the SIL is higher and that should not be. The experts who are responsible for hazard analysis and risk often decide to increase the safety integrity requirements of the central PLC unit.

Increased safety requirements on the system can also have a positive effect on the availability of that system. To meet higher security requirements in combination with hardware fault tolerance, need to have a higher fraction of failures that are safe, a programmable system is achieved through self-diagnostics. In combination with a redundant diagnostic result can also be used to increase availability.

In addition to the accumulation of risk, the probability of joint occurrence of false travel process which is not desirable because a fail-safe from the PLC system is a common argument to increase the reliability of the system by improving its diagnostic coverage (DC). Clearly, any real security system will always have a chance of physical failure. However, this failure does not necessarily have to produce the trip at that time because the internal diagnostic system failure is observed.

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